ATmega128 datasheet(17/386 Pages) ATMEL

17 / 386 page

2467S–AVR–07/09

ATmega128

When using the SEI instruction to enable interrupts, the instruction following SEI will be exe-

cuted before any pending interrupts, as shown in this example.

Interrupt Response

Time

The interrupt execution response for all the enabled AVR interrupts is four clock cycles mini-

mum. After four clock cycles, the program vector address for the actual interrupt handling routine

is executed. During this 4-clock cycle period, the Program Counter is pushed onto the Stack.

The vector is normally a jump to the interrupt routine, and this jump takes three clock cycles. If

an interrupt occurs during execution of a multi-cycle instruction, this instruction is completed

before the interrupt is served. If an interrupt occurs when the MCU is in Sleep mode, the inter-

rupt execution response time is increased by four clock cycles. This increase comes in addition

to the start-up time from the selected sleep mode.

A return from an interrupt handling routine takes four clock cycles. During these 4-clock cycles,

the Program Counter (two bytes) is popped back from the Stack, the Stack Pointer is incre-

mented by two, and the I-bit in SREG is set.

Assembly Code Example

sei

; set global interrupt enable

sleep

; enter sleep, waiting for interrupt

; note: will enter sleep before any pending

; interrupt(s)

C Code Example

__enable_interrupt(); /* set global interrupt enable */

__sleep(); /* enter sleep, waiting for interrupt */

/* note: will enter sleep before any pending interrupt(s) */

ATmega128 Datasheet(PDF) 17 Page - ATMEL Corporation